This invention relates generally to the field of structures for applying marking fluids of various types, including structures for use in marking stamps, such as hand stamps or other printing members, and ink pads, ink rolls, and other devices for applying ink to a marking or printing implement. Specifically, this invention relates to marking structures of the type containing their own essentially permanent supply of marking fluid, such that, for example, repetitive re-inking of the marking surface is unnecessary.
U.S. Pat. Nos. 2,777,824 and 3,055,297, both to Harry R. Leeds, disclose marking structures made of highly porous plastic material, the pores of which are of microscopic proporations and are filled with a marking fluid such as ink. Structures made in accordance with the teachings of the Leeds patents have experienced a high degree of commercial success as hand stamps, stamp pads, and also as ink rolls such as are used for applying ink to printing members in automatic printing equipment. Such structures are advantageous because of their long life, both in length of time and in numbers of operations or impressions, and because they operate well without the necessity of repetitive re-inking of the marking surface. Such structures apply ink in a uniform and reliable fashion. For example, hand stamps made using such structures, which have various characters or designs molded at their surface, provide sharp and uniform impressions with high definition and uniformity. As stamp pads, such structures place a uniform layer of ink on a marking device, such as a rubber stamp, and are reliable over long periods of time. Similarly, as ink rolls, such structures provide uniform inking of printing members and exhibit fast recovery to facilitate repetitive use over long periods of time.
However, there are certain problems and difficulties with microporous structures of this type. In particular, structures made according to the disclosures of U.S. Pat. Nos. 2,777,824 or 3,055,297 have exhibited a significant degree of dimensional instability. For example, during the useful lifetime of a hand stamp using such structures, the structure will undergo perceptible shrinkage, on the order of as high as 15-20 percent of its original size, by linear dimensions.
Another problem relates to the strength and integrity of structures made in accordance with the teachings of the Leeds patents. If undue stresses are placed on such structures, particularly shearing stresses on corners or on characters molded on the surfaces thereof, there is an occasional tendency for crumbling or breakage of small portions from the structure.
Another problem relates to the process of manufacture. For example, in the case of hand stamps, the total processing time may be a period on the order of about 15 hours. A lengthy period of time is primarily required for a "curing" step, in which the molded and sealed structure reaches an initial dimensional stability.
Macroporous ink-containing marking structures, such as those made of porous rubber, vinyl or urethane foam, do not have these problems. However, the overall quality and performance of such marking devices are considerably inferior to those made in accordance with the disclosures of the aforementioned Leeds patents. Specifically, such structures are known to have significant aging problems, form the standpoints of time and numbers of operations. Product life is quite short. Their resistance to high temperatures and humidity is low and dry-out is a significant problem. In printing members using such structures, there is often over-inking which produces a significant degree of feathering, wicking, bleeding and strike-through, all problems well-known to those skilled in the art.
My invention overcomes each of the aforementioned problems. The inventive structure normally undergoes shrinkage of no more than about 3-5% during its useful lifetime. Further, the inventive structures have greatly increased strength which drastically reduces the likelihood of crumbling or breakage.
In addition, the time required to produce the structures of this invention is only a fraction of that required in the prior art -- the total processing time being about two hours for a typical hand stamp, primarily because no lengthy "curing" step is necessary.
In addition, the inventive structures have a substantially increased lifetime with respect to all structures known in the prior art. For example, while a typical hand stamp made in accordance with the teachings of the above-mentioned Leeds patents would have a useful lifetime on the order of 20,000 impressions, the useful lifetime of a comparable hand stamp which includes the inventive structure is on the order of 200,000 impressions, around a tenfold increase.
Another advantage over the structures disclosed in the aforementioned Leeds patents is that the inventive structure may be reloaded with marking fluid, if so desired, to further extend its usefulness.
Each of these advantages is brought about without sacrificing any of the other advantages of microporous marking structures of the type described in the above-mentioned Leeds patents.